Asyncio and coroutines confusion

async-confusing.py

import asyncio

@asyncio.coroutine
def coro():
    return "foo"


# Writing the code without a list comp works,
# even with an asyncio.sleep(0.1).
@asyncio.coroutine
def good():
    yield from asyncio.sleep(0.1)
    result = []
    for i in range(3):
        current = yield from coro()
        result.append(current)
    return result


# Using a list comp without an async.sleep(0.1)
# works.
@asyncio.coroutine
def still_good():
    return [(yield from coro()) for i in range(3)]


# Using a list comp along with an asyncio.sleep(0.1)
# does _not_ work.
@asyncio.coroutine
def bug():
    yield from asyncio.sleep(0.1)
    return [(yield from coro()) for i in range(3)]


loop = asyncio.get_event_loop()
print(loop.run_until_complete(good()))
print(loop.run_until_complete(still_good()))
print(loop.run_until_complete(bug()))


# Running this code gives:
# $ python3.4 /tmp/test.py
# ['foo', 'foo', 'foo']
# ['foo', 'foo', 'foo']
# <generator object <listcomp> at 0x104eb1360>
#
# I don't understand why the third function is different.